The present invention relates to data storage media. More particularly, the present invention relates to the self-servowriting of servo patterns on storage media.
Self-servowriting has become an attractive technique for producing servopatterns on disk files because it eliminates the need for costly, external positioning systems, and can be performed outside of a clean room environment. In general, this technique involves using the read and write elements installed on the actuator of the disk drive xe2x80x9cin-situxe2x80x9d to initially write the servopattern, which is thereafter used to correctly position the actuator during drive operation by a user.
Techniques for self-propagation of both radial positioning servopatterns and circumferential timing patterns have been developed recently. For example, in commonly assigned U.S. Pat. No. 5,659,436 entitled xe2x80x9cRadial Self-Propagation Pattern Generation for Disk File Servowritingxe2x80x9d (incorporated by reference herein in its entirety) the servo position signal used to control the head location while writing the next servo track is derived from the readback amplitude of a single track written one step earlier. The process begins with the actuator held against a limit stop called the crashstop. A track is written, and the read element steps forward a small distance to servo at a point on the leading edge of the written track at which the amplitude has dropped by some predetermined fractional amount.
In modern disk files, however, the read element can be offset from the write element on the actuator by as much as several tracks. When this read-to-write element offset gets large, it becomes desirable to use a combination of readback amplitudes from several earlier-written tracks to provide the position signal for the next track as described in commonly assigned U.S. Pat. No. 5,757,574 (incorporated by reference herein in its entirety) entitled xe2x80x9cMethods and Systems for Self-Servowriting Including Maintaining a Reference Level Within a Usable Dynamic Rangexe2x80x9d and in the commonly assigned, concurrently filed Application entitled xe2x80x9cTechniques For Multitrack Positioning and Controlling Error Growth in Self-Servowriting Systemsxe2x80x9d (also incorporated by reference herein in its entirety). In such cases, especially when the read-to-write offset is especially large (so that the write element cannot xe2x80x9creachxe2x80x9d the first few tracks to write an initial propagation pattern when the head is against the crashstop), a need exists for providing an initial set of written tracks that can be used for subsequent multitrack servo and self-propagation.
The initial set of tracks is written in accordance with a first aspect of the present invention in which the actuator is moved against a compliant structure (e.g., crashstop) with a first force applied thereto to hold the actuator in a first position to write a first track of the servopattern. The force is changed, thereby reaching a second position of the actuator against the compliant structure, at which a second track of the servopattern is written.
The process is iterated for additional tracks. The distances (i.e., overlap) between pairs of written tracks are measured using a read element of the actuator, and this measured distance is compared to predetermined, desired distance. If the measured distance is within a specified tolerance, the process is complete; and if not, the tracks are erased and the process is repeated with changed forces applied to the actuator against the crashstop resulting in modified distances between tracks.
The present invention overcomes the problem of self-servowriting an initial set of tracks, especially when the read element is separated from the write element (i.e., the write element cannot reach the first few tracks) by using the compliant property of a nearby structure (e.g., a crashstop) which provides temporary positioning over the first few tracks, and which allows the write element to reach those tracks.